Various government and international regulations are in force or are being investigated to minimize particulate generation. For gasoline direct injection (GDI) it is particularly important to obtain a very precise spray pattern in order to minimize particulate production.
One problem with direct injection and GDI in particular is that deposits build up on a tip portion of each fuel injector due to its exposure to the combustion process.
In order to obtain the precise spray patterns required the fuel injectors have to be produced with very detailed structures such as sharp edges and these are affected by the build-up of coke deposits on the tip portion of the fuel injector resulting in increased soot production. The coke deposits are generally of a carbon based nature and are produced as by-products of the combustion process.
In addition, because the coke deposits are porous in nature, fuel can soak into the coke deposit and is then burnt late in the combustion process resulting in the production of soot.
In order to reduce or eliminate such coking it is known from, for example, Japanese Patent Publication JP-A-59041662 to provide a catalytic coating on the injector tip portion of a fuel injector to promote the reduction in the build-up and/or removal of the coke deposits.
The applicants have found that under normal working conditions when the engine is under load such a catalytic coating is effective in reducing coke build-up and in facilitating the removal of such deposits during operation of the engine.
It is however a problem that the catalytic material is not very effective at light loads or in repetitive stop start conditions where coking can form due to the relatively low temperature of the tip portion of the fuel injector in such conditions.
The above problem is solved according to a first aspect of the invention there by providing an engine system that comprises a direct injection engine having a cylinder in which a piston is slidingly supported to form in combination with a cylinder head a combustion chamber, a fuel injector for the cylinder having a catalytic coated tip portion that projects into the combustion chamber and an electronic controller to control the operation of the engine and operates the engine in a heating mode of operation if heating of the fuel injector tip is requested.
If heating of the injector tip portion is not requested, the electronic controller may be operable to operate the engine in a normal mode of operation.
Heating of the fuel injector tip may be required if the temperature of the catalytic coated tip portion is below a light-off temperature of the catalytic material.
Heating of the fuel injector tip may be required if the temperature of the catalytic coated tip portion is below a light-off temperature of the catalytic material and de-coking of the injector tip is required.
Operating the engine in the heating mode may comprise increasing the temperature of combustion by using the electronic controller to adjust at least one of the timing the injection of fuel and the quantity of fuel injected into the combustion chamber.
The engine may be a multi-cylinder engine. In which case, operating the engine in the heating mode comprises using the electronic controller to disable at least one of the cylinders of the engine so as to increase the loading on each cylinder still operating.
The cylinders of the engine may be disabled in a predetermined sequential order.
Each disabled cylinder may be arranged to pump air while it is disabled.
Operating the engine in the heating mode may comprise operating at least one cylinder rich of stoichiometric and at least one cylinder lean of stoichiometric so as to promote an increased combustion temperature and an oxidizing environment in the at least one lean operated cylinder.
Operating the engine in the heating mode may comprise operating at least one cylinder lean of stoichiometric and at least one cylinder leaner than the at least one lean of stoichiometric operating cylinder so as to promote an increased combustion temperature in the at least one leaner operated cylinder.
The engine may be a spark ignited engine and operating the engine in the heating mode may comprise increasing the temperature of combustion by using the electronic controller to adjust the timing of the ignition to one of retarded and advanced relative to a normal timing position.
According to another aspect of the invention there is provided a method of operating a direct injection combustion engine, each cylinder of the engine having a fuel injector with a catalytic coated tip portion that is exposed to the products of combustion; comprising operating the engine in a heating mode of operation in response to a request to heat the fuel injector tip.
If heating of the fuel injector tip portion is not requested, the method may comprise operating the engine in a normal mode of operation.
Heating of the fuel injector tip may be requested if the temperature of the catalytic coated tip portion is below a light-off temperature of the catalytic material.
Heating of the fuel injector tip may be requested if the temperature of the catalytic coated tip portion is below a light-off temperature of the catalytic material and de-coking of the injector tip is required.
Operating the engine in the heating mode may comprise adjusting at least one of the timing the injection of fuel and the quantity of fuel injected into each operating cylinder.
The engine may be a multi-cylinder engine. In which case, operating the engine in the heating mode may comprise disabling at least one of the cylinders of the engine so as to increase the loading on the cylinders still operating.
The cylinders of the engine may be disabled in a predetermined sequential order.
Each disabled cylinder may be arranged to pump air while it is disabled.
Operating the engine in the heating mode may comprise operating at least one cylinder rich of stoichiometric and at least one cylinder lean of stoichiometric so as to promote an increased combustion temperature and an oxidizing environment in the at least one lean operated cylinder.
Operating the engine in the heating mode may comprise operating at least one cylinder lean of stoichiometric and at least one cylinder leaner than the at least one lean of stoichiometric operating cylinder so as to promote an increased combustion temperature in the at least one leaner operated cylinder.
The engine may be a spark ignited engine and operating the engine in the heating mode may comprise adjusting the timing of the ignition to one of retarded and advanced relative to a normal timing position for each operating cylinder.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.